A support team member says endurance swimmer Penny Palfrey has ended her effort to become the first woman to swim unassisted from Cuba to the Florida Keys, about three quarters of the way along.

Andrea Woodburn, one of the team members, says Palfrey halted her effort early Sunday about 42 kilometres south of Key West because of a strong ocean current.

Woodburn says she was in contact with Palfrey's boat and was told the swimmer had gotten out of the water right around midnight ET. Woodburn says the British-born Australian is fine but gave no further details.

Palfrey had been swimming steady and strong and reported no physical complaints other than jellyfish stings earlier in the day on the more than 160-kilometre swim, according to her support team.